1. Field of the Invention
The invention relates to a process for production of methane rich fuel gas by two-stage gasification of either caking or non-caking coals, and, more particularly, to a method and apparatus for the removal of oversized char particles that would not be carried out by the gas stream up-flow.
2. Description of the Prior Art
A method of producing methane fuel gas using a two-stage gasification process is described in my earlier U.S. Pat. No. 3,782,913. In this process steam and particulate coal are reacted in the second stage with synthesis gas from the first stage, which contains hydrogen and oxides of carbon at temperatures in excess of 1600.degree.F and pressures in excess of 50 atmospheres, to produce a product gas containing hydrogen, methane, carbon oxides, and entrained char. The product gas and entrained char are withdrawn and separated, the product gas being thereafter treated to remove carbon oxides and other diluents, and ultimately methanated to produce methane-rich fuel gas. The char is recycled to the first gasification stages for reaction with steam and oxygen at temperatures in excess of 2500.degree.F and pressures in excess of 50 atmospheres to produce a synthesis gas containing hydrogen and oxides of carbon for reaction in the second gasification stage.
The efficiency at which the coal particles and the char product particles are entrained in the up-flow gas in the second stage is a key factor affecting the overall efficiency of the process. One problem that has been encountered in this regard is that particles of some kinds of coal, generally called caking coals, tend to agglomerate as they become char product particles. Moveover, some proportion of the char product particles so formed become too large to be entrained by the product gases of the second stage. Consequently, these oversize char particles will accumulate and will tend to plug the passage for first stage synthesis gas. This problem is of considerable importance since a majority of the coals found in the Eastern United States are of a caking nature.